1. Field of the Invention
The present invention relates generally to agricultural implements such as agricultural planters. More particularly, the present invention relates to an agricultural implement having at least one ground engaging tool supported on an implement frame and a fluid circuit to control movement of the implement frame between working and transport positions. Even more particularly, the present invention is directed to a fluid control circuit for controlling movement of the implement frame, having an upper depth stop valve with a bypass in communication with a hydraulic cylinder to allow controlled upward movement of the tool frame between a field transport position and a road transport position.
2. Discussion of the Related Art
Conventional planters typically include a series of evenly spaced row planter units connected to an implement frame and/or tool bar so as to be towed across a field. The row planter units are generally configured to plant particulate product (i.e., seed, herbicide, pesticide, fertilizer, etc.) in evenly spaced individual rows. The planter is usually towed by a propelling vehicle such as a tractor or other prime mover across the field. As the planter reaches the end of a row, or requires transport from a field to another more remote location, it is often necessary to reconfigure the planter from a field planting configuration or position to a field transport, row transport or headland position (for movement between planting rows), or a road transport position.
In many prior art systems, hydraulic lift systems are utilized to reconfigure the planter to and from the above noted positions. A rockshaft, tool bar or a similarly moveable member is mounted to the implement frame so as to support and move one or more such ground engaging tool. Movement of the implement frame, and thus the tools, is typically accomplished using at least one hydraulic cylinder operatively extending between the frame and the moveable member. As such, the moveable member can be raised and lowered so as to engage the tools with the ground or be configured for transport.
In such prior art systems, remote hydraulic valves provide hydraulic flows to locations on the moveable member to adjust the positioning of the same. The valves are controlled in an operator station in the cab of the vehicle, most commonly by manipulating a control device that provides a signal and indicates a desired flow rate to or from the hydraulic valve. The hydraulic valves are typically connected to a manifold or manifolds, most commonly located at the rear of the vehicle, to which hydraulic actuators are mounted. The hydraulic actuators include such things as hydraulic motors and cylinders. By manipulating the control device, the operator can vary the flow direction and the flow rate to the manifold, and hence to the hydraulic actuators located on the implement.
However, known hydraulic systems have drawbacks. For example, in most prior art systems, the maximum road transport position or height (height used herein means the clearance of the tool frame from the ground) and the field transport height is often the same. This is due to the fact that when an operator strokes a master cylinder controlling the height of the implement, the cylinders typically bottom out thereby limiting the maximum raised height of the planter from the ground. The limited maximum height of the road transport position has proved problematic when the planter needs to be moved long distances over ditches and other uneven surfaces. Portions of the planter may not have adequate clearance to cross these uneven surfaces. Likewise, the height (clearance of the implement frame from the ground) of the field transport position in many of these systems is unnecessarily high. As the field transport position most commonly only requires turning between adjacent rows, it is unnecessary to raise the system to the same height required for road transport.
Even in those systems that can achieve different road transport and field transport heights, there is not an adequate system to control the movement of the implement from the field transport to the road transport position. In many systems there is not an adequate upper stop. As a result, the implement frame may be raised to or near a road transport position when only a field transport height is needed. It is desirable to not only control the transition between a field transport position and a road transport position, but to also provide an upper depth or height stop once the tool frame has reached the field transport position as improper or haphazard movement between the field transport and the road transport positions can damage equipment. Furthermore, it is often unnecessary and time consuming to raise the tool frame to a fully raised position during planting operations. As such, it is preferable to have a system wherein movement between a field transport and planting position can be achieved quickly and stopped before moving into a road transport position, while at the same time controlled steady movement between the field transport and the road transport positions can be achieved when necessary.
There have been some attempts at providing a planter wherein controlled movement between distinct field transport and road transport configurations can be achieved. For example, one known system allows for an upper depth stop functionality via a series of complex electronic controls. This system, while somewhat satisfactory for its intended purpose, exhibits drawbacks as the electronic upper depth stop system is overly complex and costly to manufacture.
Therefore, there is a need or desire for a hydraulic control system for a work vehicle such as a planter to address the drawbacks described above. The hydraulic control system should also be configured to be utilized with a wide variety of bar supported implements frames and/or vehicles in addition to those related to agriculture. The hydraulic control system should also be versatile so as extend its lifetime and minimize replacement. Also, the hydraulic system should be simple in design so as to reduce costs associated with labor and manufacturing.